The present invention relates to stabilization of the amplitude of a horizontal sweep signal for projection apparatus, and, more particularly, to crystal stabilization of the horizontal sweep of light valve projection apparatus while also maintaining proper or desired color rendition.
Light valve projection apparatus typically may be employed to project an image onto a display device such as a flat or curved screen, which may include a rear projection screen, the inside of a dome that may be used for pilot training, or other suitable and/or desirable surfaces. The light valve itself generates images to be projected in response to electronic signals that are received from a remote source and are typically arranged so that the image is scanned, such as in a raster, in conformance with a code or standard, such as NTSC (present TV standard in the United States), wherein the horizontal sweep time for one horizontal line is about 63.5 microseconds, or MACII (a computer display format), wherein the horizontal sweep time for one horizontal line is about 27 microseconds.
In certain situations, such as for displaying wide panoramic scenes with fine detail, it may be desirable to use simultaneously more than one projection apparatus for projecting images, with the resulting images being optically, mechanically and electronically directed to abut, and to be in registration with, a corresponding neighboring image along a vertical edge, that is, along the beginning or ending of the horizontal sweeps.
For example, as viewed from the light valves in the direction of projection, the right vertical edge (endings of horizontal sweeps) of a left image may be arranged to abut the left vertical edge (beginnings of horizontal sweeps) of a right image. For these multiple image displays, it is necessary to maintain a constant horizontal size of both the left and right images as projected, otherwise the abutting vertical interface will not be constant and a gap between the desired abutting vertical edges or an excessive overlap between same, or some fluctuation between a gap and overlap nominally in the area of the desired abutment, will occur. Factors tending to cause variation in horizontal size include temperature variations of the light valve and its components, and to a lesser degree aging of the components. Such factors also include temperature and humidity variations of the electronic sweep circuitry, and to a lesser degree aging of the components thereof. In particular, these variations are more severe, but not limited to, high voltage, electrostatic sweep systems.
A present scheme for regulating horizontal (hereinafter referred to as "H") size includes using one of the color carrier frequencies (red, green, blue), for regulating H-size. This scheme maintains constant colorimetry (i.e., exact rendition of received color), but permits the H-size to vary directly with variations in the regulating color carrier frequency. In this scheme it is difficult to regulate the color carrier frequency inasmuch as the color carrier signal generator is keyed to obtain phase coherency of the color carrier signal at the beginning of each raster line and the frequency settling time would interfere with such regulation.
Any attempt to regulate H-size should give consideration to the adverse effects such regulation may have on color rendition and make provisions to compensate therefor. It would also be desirable to have independence between color and H-size adjustments so that the one having more importance for a particular application may be used for exact adjustment while the other adjustment may be used to readjust the secondary condition should any cross-talk or coupling of one adjustment affect the other. Generally color may be considered to be more critical for TV, VCR, etc. type sources, while H-size may be deemed to be more important for simulation type source's. However, it is still desirable to achieve accurate color rendition regardless of the source of data.
Accordingly, it is an object of the present invention to provide apparatus and method for maintaining a constant horizontal size of a raster for an image generated by a light valve projection apparatus.
Another object of the present invention is to provide apparatus and method for maintaining a constant horizontal size of a raster for an image produced by light valve projection apparatus while also maintaining proper and/or desired color rendition of the image.
Yet another object of the present invention is to provide apparatus and method for maintaining a constant horizontal size of the raster while maintaining proper and/or desired color rendition wherein the size may be adjusted as desired.